∏ = 3.141592653589793238462...
How many times in Maths class did/do you ever wonder when in the hell you'd actually need to know equations like this in real life? Well, to my dismay, it turns out that when you like to make stuff, Maths is kind of fundamental. Especially when it comes to making circle skirts. One of the easiest and quickest garments you can whip up on your machine, provided you can first figure out the radius of your waistline circumference... Ugh. Fear not, my mathematically challenged friends - we have figured it out for you. And made some pretty skirts along the way!
Ready class? Then let's begin.
We're going back to GCSE Maths here guys. Remember pi?? That crazy 3 with endless decimal places is what we need to figure out the radius of our waistline circumferences. And why exactly do we need to know the radius? We need the radius in order to measure, mark out and cut the perfect little circle -that will be our waistline- onto the fabric. Without the radius, the only way to mark out the curve would be by shaping your measuring tape into a quarter circle on your folded piece of fabric (this ad hoc method I wouldn't even suggest to lazy stitchers as the results would inevitably be inaccurate, leading to a whole lot of time consuming fixing and tweaking and hair pulling and fabric wasted...).
For each type of circle skirt, be it full circle, half circle or quarter circle, the mathematical equation we need in order to find out the radius will be slightly different. Before we look at each one individually, we first need to know the foundation equation: Circumference (c) + two lots of seam allowance (3.2cm) ÷ ∏ (3.14) = diameter (radius × 2). We'd also like to point out now that we will be using metric measurements ie. centimetres, not inches. Nothing against Imperial, only that our brains simply can't cope with Imperial decimals, what with them being in eighths as opposed to tens...!
A note about seam allowance: seam allowance needs to be added on to both your waistline seam and side seams. For the waistline, we will be subtracting 1.6cm from your final radius measurement. For the side seams, we add 1.6cm for each raw edge to be seamed to your initial waistline circumference measurement: half and quarter circle skirts will have only one back seam so add 3.2cm to your waistline; a full circle skirt cut from 2 pieces will have 2 side seams so add 6cm altogether).
Full circle skirt
Let us begin by pointing out that it is unlikely you will be able to cut a whole circle skirt from a standard piece of 45" width fabric (unless making a miniskirt). The following diagram assumes that you will be cutting 2 semi-circles and joining them at the side seams, with your zipper inserted into one of those side seams - please see our invisible zipper tutorial when you get to that part!
Example: Your waistline measures 66cm (equivalent of a 26" waist). You are making a full circle skirt from 2 semi circles so you need to factor in the 4 raw edges that will be your 2 side seams. 66cm (C) + 6.4cm (4SA) = 72.4cm. 72.4cm ÷ 3.14 = 23cm (diameter). (23cm ÷ 2) - 1.6cm (waistline seam allowance) = 9.9cm (radius).
Tip: cut a piece of string the length of your final radius measurement and holding one end at the corner, use it to accurately mark out your curve.
Half circle skirt
Our waistline measurement now becomes a semi-circle, so in order to find the radius with our little equation we need to double the waist measurement.
Example: (66cm x 2) = 132cm (2C) + 3.2cm (2SA) ÷ 3.14 = 43cm (diameter). (43 ÷ 2) - 1.6cm (SA) = 19.9cm (radius).
Tip: before hemming your circle skirt it's a great idea to put it on a mannequin and leave it to "drop" overnight. Seeing as parts of a circle skirt hang on the bias, they'll need some time to stretch out naturally so you can then sew an even hem. If you don't give the fibres time to drop, you'll end up with a wavy, uneven hem line.
Quarter circle skirt
Just as we doubled the waistline as we halved the circle skirt, so we need to quadruple the waistline for a quarter circle skirt. The following diagram shows the quarter circle piece being cut from a single piece of fabric, no fold.
Example: (66cm x 4) + 3.2cm (2SA) = 267.2cm ÷ 3.14 = 85cm (diameter). (85 ÷ 2) - 1.6cm (SA) = 40.9cm (radius).
Phew... Broken out in a bit of a mental sweat there guys, and words like radius and circle have lost all meaning. We hope this has fully explained the maths behind constructing circle skirts and their variations - if not, let us know and we'll do our best to clarify anything further. We leave you with the pretty fruits of our experiments...and one final tip: hemming a curve can be tricky; try our rolled hem tutorial for a quick, slick finish!
Over and out x